Focus control method and video camera apparatus

ABSTRACT

Focus control is provided by estimating an estimation value by extracting a high-frequency component of a video signal for each focus lens position. The correct focus lens position for focusing a target object is determined as that focus lens position where the estimation value for a plurality of conditions at a particular focus lens position becomes maximum. The estimation value is determined to be maximum when, for successive focus lens positions, the estimation value decreases continuously. The various conditions for imaging, according to an aspect of the focus control, includes the filter coefficients for extracting the high-frequency component of the video signal and the size of the windows from which the video signal is imaged. The estimation value for each focus lens position is determined for these various conditions for imaging and a predetermined weight is allocated thereto, wherein the estimation value is determined to increase when the weighted sum indicating an increase outweighs that for a decrease.

TECHNICAL FIELD

The present invention relates to a focus control method of focusing alens on an object upon an image pickup thereof and a video cameraapparatus for focusing its lens on the object by using the focus controlmethod.

BACKGROUND ART

A consumer video camera has employed an autofocus method ofautomatically focusing a lens on an object.

It is well known that, in order to discriminate whether or not a lens isin focus or out of focus, it is sufficient to discriminate whethercontrast of a video signal obtained by an image pickup is high or low.In other words, if the contrast is high, then the lens is in focus. Ifon the other hand the contrast is low, then the lens is out of focus. Ahigh-frequency component is extracted from the video signal obtained byan image pickup, and a data obtained by integrating the high-frequencycomponent in a predetermined set area is generated. It is possible todiscriminate whether the contrast is high or low, by using theintegrated data. The integrated data is indicative of how much there isthe high-frequency component in the predetermined area. In general, thisdata is called an estimation value. Accordingly, it is possible torealize the autofocus method by driving a focus lens so that theestimation value should be maximum (i.e., the contrast should bemaximum).

The estimation value extracted by the above method inevitably includes aplurality of factors in response to a state of an object upon the imagepickup thereof. Hence, it is impossible to precisely determine a focusdeviation amount based on the estimation value. Such estimation valueinevitably includes a noise corresponding to an image pickup conditionas an element thereof, and hence it is difficult to precisely extract afocus deviation, which is fundamentally necessary, amount from suchestimation value. Therefore, since it is impossible for a conventionalfocus controlling apparatus and a conventional video camera to obtain aprecise estimation value, it takes a considerable time for theconventional focus controlling apparatus and the conventional videocamera to search for a maximum point of an estimation value. As aresult, a camera man must continue taking a blurred picture while theabove conventional focus controlling apparatus or the above conventionalvideo camera is carrying out a focusing operation.

For example, it is sometimes observed that an image picked up by a videocamera apparatus for use in a broadcasting station or for professionaluse is transmitted on the air as a live relay broadcast. If it issometimes observed that in such live relay broadcast the satisfactoryaccuracy of the estimation value is not achieved and hence it takes aconsiderable time to carry out the autofocus operation, a video signalindicative of a blurred picture is transmitted on air. Therefore, asimplified, inexpensive and small autofocus apparatus such as that usedin a consumer video camera is not necessary for the video camera for usein the broadcasting station or for professional use, but a high-accuracyfocus control and a high-speed focus control are required therefor.

It is an object of the present invention to make it possible to generatean estimation value corresponding to an image pickup condition and todetect a focus position at high speed.

DISCLOSURE OF THE INVENTION

According to the present invention, a focus control method includes anestimation-value generating means for generating an estimation value byextracting a high-frequency component in a predetermined range of avideo signal output from an imaging means while a focus lens is beingmoved, and a change detecting means for detecting change of theestimation value from the estimation-value generating means to therebydetermine a maximum point of the estimation value. The maximum point isdetermined as a focus position when an estimation value is continuouslydecreased from a focus lens position determined as the maximum point bythe change detecting means to a position whose distance therefrom is aslong as a predetermined multiple of a focal depth of a focus lens.

According to the present invention, a video camera apparatus includes anestimation-value generating means for generating an estimation value byextracting a high-frequency component in a predetermined range of avideo signal output from an imaging means while a focus lens is beingmoved, and a change detecting means for detecting change of theestimation value from the estimation-value generating means to therebydetermine a maximum point of the estimation value. The maximum point isdetermined as a focus position when an estimation value is continuouslydecreased from a focus lens position determined as the maximum point bythe change detecting means to a position whose distance therefrom is aslong as a predetermined multiple of a focal depth of a focus lens.

According to the present invention, it is possible to focus a lens on anobject to be imaged at high speed.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram showing an entire arrangement of a video camera towhich an autofocus apparatus is applied;

FIG. 2 is a diagram showing a specific arrangement of an autofocuscontrolling circuit 34;

FIG. 3 is a diagram showing a specific arrangement of ahorizontal-direction estimation value generating circuit 62;

FIG. 4 is a diagram showing a specific arrangement of avertical-direction estimation value generating circuit 63;

FIGS. 5A and 5B is a table showing a filter coefficient α and a windowsize set for respective circuits of the horizontal-direction estimationvalue generating circuit 62 and the vertical-direction estimation valuegenerating 63;

FIGS. 6A and 6B is a diagram used to explain the respective windowsizes;

FIG. 7 is a table showing weight data W set for respective estimationvalues E;

FIGS. 8 to 13 are flowcharts used to explain an autofocus operation;

FIG. 14 is a diagram showing a movement of a lens when a lens movementdirection is determined in order to focus the lens on an object;

FIGS. 15A and 15B is a diagram showing a state that a non-target objectlies in a window;

FIG. 16 is a diagram showing fluctuation of estimation values stored ina RAM 66 when the lens movement direction is determined;

FIG. 17 is a table showing data stored in the RAM 66 during theautofocus operation; and

FIG. 18 is a graph showing change of the estimation values obtained uponthe autofocus operation.

BEST MODE CARRYING OUT THE INVENTION

Initially, a focus control method and a video camera employing the abovefocus control method according to an embodiment of the present inventionwill hereinafter be described with reference to FIGS. 1 to 18.

A total arrangement of the video camera apparatus according to thepresent invention will be described with reference to FIG. 1. The videocamera apparatus includes a lens block 1 for optically condensingincident light to the front of an imaging device, an imaging block 2 forconverting light incident from the lens block into RGB electric videosignals obtained by an image pickup, a signal processing block 3 forsubjecting the video signals to a predetermined signal processing, and aCPU 4 for controlling the lens block 1, the imaging block 2, and thesignal processing block.

The lens block 1 is detachably provided in a video camera apparatusbody. This lens block 1 includes, as optical elements, a zoom lens 11for, by moving along an optical axis, continuously change a focal lengthwithout changing a position of an image point to thereby zoom an imageof an object, a focus lens 12 for bringing the object into focus, and aniris mechanism 13 for adjusting an amount of light incident on the frontof the imaging device by changing its aperture area.

The lens block 1 further includes a position detecting sensor 11a fordetecting an optical-axis direction position of the zooming lens 11, adrive motor 11b for moving the zooming lens 11 in the optical-axisdirection, a zoom-lens drive circuit 11c for supplying a drive controlsignal to the drive motor lib, a position detecting sensor 12a fordetecting an optical-axis direction position of the focus lens 12, adrive motor 12b for moving the focus lens 12 in the optical-axisdirection, a focus-lens drive circuit 12c for supplying a drive controlsignal to the drive motor 12b, a position detecting sensor 13a fordetecting an aperture position of the iris mechanism 13, a drive motor13b for opening and closing the iris mechanism 13, and an iris mechanismdrive circuit 13c for supplying a drive control signal to the drivemotor 13b.

Detection signals from the position detecting sensors 11a, 12a, 13a arealways supplied to the CPU 4. The zooming lens drive circuit 11c, thefocus lens drive circuit 12c, and the iris mechanism drive circuit 13care electrically connected to the CPU 4 so as to be supplied withcontrol signals from the latter.

The lens block 1 has an EEROM 15 for storing a focal length data of thezoom lens 11 and an aperture ratio data thereof, a focal length data ofthe focus lens 12 and an aperture ratio thereof, and a manufacturer nameof the lens block 1 and a serial number thereof. The EEPROM 15 isconnected to the CPU 4 so that the respective data stored therein areread out therefrom based on a read command from the CPU 4.

The imaging block 2 has a color separation prism 21 for color-separatingincident light from the lens block 1 into three primary-color lights ofred (R), green (G) and blue (B) and imaging devices 22R, 22G and 22B forconverting lights of R component, G component and B component, which areobtained by separating light at the color separation prism 21 and arefocused on image surfaces thereof, into electric video signals (R), (G),(B) to output the signals. Each of these imaging devices 22R, 22G and22B is formed of a CCD (charge Cupled Device), for example.

The imaging block 21 has preamplifiers 23R, 23G, 23B for respectivelyamplifying levels of the video signals (R), (G), (B) output from theimaging devices 22R, 22G, 22B and for carrying out correlated doublesampling for removing a reset noise.

The imaging block 2 further has a timing signal generating circuit 24for generating a VD signal, an HD signal and a CLK signal each servingas a basic clock used for operation of each of circuits in the videocamera apparatus based on a reference clock from a reference clockcircuit provided therein, and a CCD drive circuit 25 for supplying adrive clock to the imaging device 22R, the imaging device 22G and theimaging device 22B based on the VD signal, the HD signal and the CLKsignal supplied from the timing signal generating circuit. The VD signalis a clock signal representing one vertical period. The HD signal is aclock signal representing one horizontal period. The CLK signal is aclock signal representing one pixel clock. The timing clock formed ofthese VD, HD and CLK signals is supplied to each of the circuits in thevideo camera apparatus through the CPu 4, though not shown.

The signal processing block 3 is a block provided in the video cameraapparatus for subjecting the video signals (R), (G), (B) supplied fromthe imaging block 2 to a predetermined signal processing. The signalprocessing block 3 has A/D converter circuits 31R, 31G, 31B forrespectively converting the analog video signals (R), (G), (B) intodigital video signals (R), (G), (B), gain control circuits 32R, 32G, 32Bfor respectively controlling gains of the digital video signals (R),(G), (B) based on a gain control signal from the CPU 4, and signalprocessing circuits 33R, 33G, 33B for respectively subjecting thedigital video signals (R), (G), (B) to a predetermined signalprocessing. The signal processing circuits 33R, 33G, 33B have kneecircuits 331R, 331G, 331B for compressing the video signals to a certaindegree or more, γ correction circuits 332R. 332G, 332B for correctingthe levels of the video signals in accordance with a preset γ curve, andB/W clip circuits 333R, 333G, 333B for clipping a black level smallerthan a predetermined level and a white level larger than a predeterminedlevel. Each of the signal processing circuits 33R, 33G, 33B may have aknown black γ correction circuit, a known contour emphasizing circuit, aknown linear matrix circuit and so on other than the knee circuit, the γcorrection circuit, and the B/W clip circuit.

The signal processing block 3 has an encoder 37 for receiving the videosignals (R), (G), (B) output from the signal processing circuits 33R,33G, 33B and for generating a luminance signal (Y) and color-differencesignals (R-Y), (B-Y) from the video signals (R), (G), (B).

The signal processing block 3 further has a focus control circuit 34 forreceiving the video signals (R), (G), (B) respectively output from thegain control circuit 32R, 32G, 32B and for generating an estimation dataE and a direction data Dr both used for controlling the focus based onthe video signals (R), (G), (B), an iris control circuit 35 forreceiving the video signals (R), (G), (B) respectively output from thesignal processing circuits 33R, 33G, 33B and for controlling the irisbased on the levels of the received signals so that an amount of lightincident on each of the imaging devices 22R, 22G, 22B should be a properamount of light, and a white balance controlling circuit 36 forreceiving the video signals (R), (G), (B) respectively output from thesignal processing circuits 33R, 33G, 33B and for carrying out whitebalance control based on the levels of the received signals.

The iris control circuit 35 has an NAM circuit for selecting a signalhaving a maximum level from the supplied video signals (R), (G), (B),and divides the selected signal with respect to areas of a picturecorresponding thereto to totally integrate each of the video signalscorresponding to the areas of the picture. The iris control circuit 35considers every illumination condition of an object such as backlighting, front lighting, flat lighting, spot lighting or the like togenerate an iris control signal used for controlling the iris, andsupplies this iris control signal to the CPU 4. The CPU 4 supplies acontrol signal to the iris drive circuit 13c based on the iris controlsignal.

The white balance controlling circuit 36 generates a white balancecontrol signal from the supplied video signals (R), (G), (B) so that thegenerated signal should satisfy (R-Y)=0 and (B-Y)=0, and supplies thiswhite balance control signal to the CPU 4. The CPU 4 supplies a gaincontrol signal to the gain controlling circuits 32R, 32G, 32B based onthe white balance control signal.

The focus control circuit 34 will hereinafter be described in detailwith reference to FIG. 2.

The focus control circuit 34 has a luminance signal generating circuit61, a horizontal-direction estimation value generating circuit 62, avertical-direction estimation value generating circuit 63, and amicrocomputer 64.

The luminance-signal generating circuit 61 is a circuit for generating aluminance signal from the supplied video signals R, G, B. In order todetermine whether the lens is in focus or out of focus, it is sufficientto determine whether the contrast is high or low. Therefore, sincechange of the contrast has no relation with change of a level of achrominance signal, it is possible to determine whether the contrast ishigh or low, by detecting only the change of a level of the luminancesignal.

The luminance-signal generating circuit 61 can generate the luminancesignal Y by subjecting the supplied video signals R, G, B to a knowncalculation based on

    Y=0.3R+0.59G+0.11B                                         (1)

The horizontal-direction estimation value generating circuit 62 is acircuit for generating a horizontal-direction estimation value. Thehorizontal-direction estimation value is a data indicating how much thelevel of the luminance signal is changed when the luminance signal issampled in the horizontal direction, i.e., a data indicating how muchcontrast there is in the horizontal direction.

The horizontal-direction estimation value generating circuit 62 has afirst horizontal-direction estimation value generating circuit 62a forgenerating a first horizontal-direction estimation value E₁, a secondhorizontal-direction estimation value generating circuit 62b forgenerating a second horizontal-direction estimation value E₂, a thirdhorizontal-direction estimation value generating circuit 62c forgenerating a third horizontal-direction estimation value E₃, a fourthhorizontal-direction estimation value generating circuit 62d forgenerating a fourth horizontal-direction estimation value E₄, a fifthhorizontal-direction estimation value generating circuit 62e forgenerating a fifth horizontal-direction estimation value E₅, a sixthhorizontal-direction estimation value generating circuit 62f forgenerating a sixth horizontal-direction estimation value E₆, a seventhhorizontal-direction estimation value generating circuit 62g forgenerating a seventh horizontal-direction estimation value E₇, an eighthhorizontal-direction estimation value generating circuit 62h forgenerating an eighth horizontal-direction estimation value E₈, a ninthhorizontal-direction estimation value generating circuit 62i forgenerating a ninth horizontal-direction estimation value E₉, a tenthhorizontal-direction estimation value generating circuit 62j forgenerating a tenth horizontal-direction estimation value E₁₀, aneleventh horizontal-direction estimation value generating circuit 62kfor generating an eleventh horizontal-direction estimation value E₁₁,and a twelfth horizontal-direction estimation value generating circuit62l for generating a twelfth horizontal-direction estimation value E₁₂.

A detailed arrangement of the horizontal-direction estimation valuegenerating circuit 62 will hereinafter be described with reference toFIG. 3.

The first horizontal-direction estimation value generating circuit 62aof the horizontal-direction estimation value generating circuit 62 has ahigh-pass filter 621 for extracting a high-frequency component of theluminance signal, an absolute-value calculating circuit 622 forconverting the extracted high-frequency component into an absolute valueto thereby obtain a data having positive values only, ahorizontal-direction integrating circuit 623 for integrating anabsolute-value data in the horizontal direction to thereby cumulativelyadd the data of the high-frequency component in the horizontaldirection, a vertical-direction integrating circuit 624 for integratingthe data integrated in the vertical direction, and a window pulsegenerating circuit 625 for supplying an enable signal used for allowingintegrating operations of the horizontal-direction integrating circuit623 and the vertical-direction integrating circuit 624.

The high-pass filter 621 is formed of a one-dimension finite impulseresponse filter for filtering the high-frequency component of theluminance signal in response to one sample clock CLK from the windowpulse generating circuit 625. The high-pass filter 621 has a cutofffrequency characteristic expressed by

    (1-Z.sup.-1)/(1-αZ.sup.-1)                           (2)

The first horizontal-direction estimation value generating circuit 62ahas a value of α=0.5 and has a frequency characteristic corresponding tothe value of α.

The window pulse generating circuit 625 has a plurality of countersoperated based on the clock signal VD representing one vertical period,on the clock signal HD representing one horizontal period and on theclock signal CLK representing one sample clock. The window pulsegenerating circuit 625 supplies the enable signal to thehorizontal-direction integrating circuit 623 based at every one sampleclock signal CLK and supplies the enable signal to thevertical-direction integrating circuit 624 at every one horizontalperiod based on the counted value of the counter. The window pulsegenerating circuit 625 of the first horizontal-direction estimationvalue circuit 62a has a counter whose count value is set so that a sizeof a window should be that of 192 pixels×60 pixels. Therefore, the firsthorizontal-direction estimation value E₁ output from thehorizontal-direction estimation value generating circuit 62 indicatesdata obtained by integrating all the high-frequency components in thewindow of 192 pixels×60 pixels.

Similarly to the first horizontal-direction estimation value generatingcircuit 62a, each of the second to twelfth horizontal-directionestimation value generating circuits 62b to 62h has a high-pass filter621, an absolute-value calculating circuit 622, a horizontal-directionintegrating circuit 623, a vertical-direction integrating circuit 624,and a window pulse generating circuit 625. A different point among therespective circuits lies in that the respective circuits (62a to 62l)have different combinations of their filter coefficients α and theirwindow sizes.

Therefore, the estimation values E₁ to E₁₂ generated by the respectivecircuits are different from one another.

FIG. 5 shows the filter coefficients a and the window sizes which arerespectively set for the first horizontal-direction estimation valuegenerating circuit 62a to the twelfth horizontal-direction estimationvalue generating circuit 62l. The reason for setting such differentfilter coefficients will hereinafter be described.

For example, the high-pass filter having a high cutoff frequency is verysuitable for use when the lens is substantially in a just focus state(which means a state that a lens is in focus). The reason for this isthat the estimation value is changed at a considerably large rate ascompared with a lens movement in the vicinity of the just focus point.Since the estimation value is changed at a small rate when the lens isconsiderably out of focus, it is not too much to say that the high-passfilter having the high cutoff frequency is not suitable for use when thelens is considerably out of focus.

On the other hand, the high-pass filter having a low cutoff frequency issuitable for use when the lens is considerably out of focus. The reasonfor this is that when the lens is moved while being considerably out offocus, the estimation value is changed at a considerably large rate.Since the estimation value is changed at a small rate when the lens ismoved in the substantial just focus state, then it is not too much tosay that the high-pass filter having the low cutoff frequency is notsuitable for use in the substantial just focus state.

In short, each of the high-pass filter having the high cutoff frequencyand the high-pass filter having the low cutoff frequency has both ofadvantage and disadvantage. It is difficult to determine which of thehigh-pass filters is more suitable. Therefore, preferably, a pluralityof high-pass filters having different filter coefficients are used andgenerate a plurality of estimation values in order to select a mostproper estimation value.

The horizontal-direction estimation value generating circuit 63according to this embodiment has plural kinds of preset windows shown inFIG. 6A. A window W1 is a window of 192 pixels×60 pixels. A window W2 isa window of 132 pixels×60 pixels. A window W3 is a window of 384pixels×120 pixels. A window W4 is a window of 264 pixels×120 pixels. Awindow W3 is a window of 768 pixels×120 pixels. A window W3 is a windowof 548 pixels×120 pixels. FIG. 6B shows windows set in thevertical-direction estimation value generating circuit 62. A window W7is a window of 120 pixels×80 pixels. A window W8 is a window of 120pixels×60 pixels. A window W9 is a window of 240 pixels×160 pixels. Awindow W10 is a window of 240 pixels×120 pixels. A window W3 is a windowof 480 pixels×320 pixels. A window W3 is a window of 480 pixels×240pixels.

It is possible to generate different estimation values corresponding tothe respective windows by setting a plurality of windows as describedabove. Therefore, regardless of a size of an object to be brought intofocus, it is possible to obtain a proper estimation value from any ofthe first horizontal-direction estimation value generating circuit 62ato the twelfth horizontal-direction estimation value generating circuit62l.

An arrangement of the vertical-direction estimation value generatingcircuit 63 will be described with reference to FIGS. 2 and 4.

The vertical-direction estimation value generating circuit 63 is acircuit for generating an estimation value in the vertical direction.The estimation value in the vertical direction is a data indicating howmuch the level of the luminance signal is changed when the luminancesignal is sampled in the vertical direction, i.e., a data indicating howmuch there is the contrast in the vertical direction.

The vertical-direction estimation value generating circuit 62 has afirst vertical-direction estimation value generating circuit 63a forgenerating a first vertical-direction estimation value E₁₃, a secondvertical-direction estimation value generating circuit 63b forgenerating a second vertical-direction estimation value E₁₄, a thirdvertical-direction estimation value generating circuit 63c forgenerating a third vertical-direction estimation value E₁₅, a fourthvertical-direction estimation value generating circuit 63d forgenerating a fourth vertical-direction estimation value E₁₆, a fifthvertical-direction estimation value generating circuit 63e forgenerating a fifth vertical-direction estimation value E₁₇, a sixthvertical-direction estimation value generating circuit 63f forgenerating a sixth vertical-direction estimation value E₁₈, a seventhvertical-direction estimation value generating circuit 63g forgenerating a seventh vertical-direction estimation value E₁₉, an eighthvertical-direction estimation value generating circuit 63h forgenerating an eighth vertical-direction estimation value E₂₀, a ninthvertical-direction estimation value generating circuit 63i forgenerating a ninth vertical-direction estimation value E₂₁, a tenthvertical-direction estimation value generating circuit 63j forgenerating a tenth vertical-direction estimation value E₂₂, an eleventhvertical-direction estimation value generating circuit 63k forgenerating an eleventh vertical-direction estimation value E₂₃, and atwelfth vertical-direction estimation value generating circuit 63l forgenerating a twelfth vertical-direction estimation value E₂₄.

A detailed arrangement of the vertical-direction estimation valuegenerating circuit 63 will hereinafter be described with reference toFIG. 4.

The first vertical-direction estimation value generating circuit 63a ofthe vertical-direction estimation value generating circuit 63 has ahorizontal-direction mean value generating circuit 631 for generating amean value data of levels of luminance signals in the horizontaldirection, a high-pass filter 632 for extracting a high-frequencycomponent of the mean-value data of the luminance signals, anabsolute-value calculating circuit 633 for converting the extractedhigh-frequency component into an absolute value to thereby obtain a datahaving positive values only, a vertical-direction integrating circuit634 for integrating an absolute-value data in the vertical direction tothereby cumulatively add the data of the high-frequency component in thevertical direction, and a window pulse generating circuit 635 forsupplying an enable signal used for allowing integrating operations ofthe horizontal-direction mean value generating circuit 631 and thevertical-direction integrating circuit 634.

The high-pass filter 632 is formed of a one-dimension finite impulseresponse filter for filtering the high-frequency component of theluminance signal in response to one horizontal period signal HD from thewindow pulse generating circuit 625. The high-pass filter 632 has thesame cutoff frequency characteristic as that of the high-pass filter 621of the first horizontal-direction estimation value generating circuit62a. The first vertical-direction estimation value generating circuit63a has a value of α=0.5 and has a frequency characteristiccorresponding to the value of α.

The window pulse generating circuit 635 has a plurality of countersoperated based on the clock signal VD representing one vertical period,the clock signal HD representing one horizontal period and the clocksignal CLK representing one sample clock supplied from the CPU 4. Thewindow pulse generating circuit 635 supplies the enable signal to thehorizontal-direction mean value generating circuit 631 based on thecounted value of the counter at every one sample clock signal CLK andsupplies the enable signal to the vertical-direction integrating circuit634 at every one horizontal period. The window pulse generating circuit635 of the first vertical-direction estimation value circuit 63a has acounter whose count value is set so that a size of a window should bethat of 120 pixels×80 pixels. Therefore, the first vertical-directionestimation value E₁₃ output from the vertical-direction estimation valuegenerating circuit 63 indicates data obtained by integrating all thehigh-frequency components in the window of 120 pixels×80 pixels.

Similarly to the above first vertical-direction estimation valuegenerating circuit 63a, each of the second to twelfth vertical-directionestimation value generating circuits 63b to 631h has ahorizontal-direction mean value generating circuit 631, a high-passfilter 632, an absolute-value calculating circuit 633, avertical-direction integrating circuit 634, and a window pulsegenerating circuit 635. A different point among the respective circuitslies in that the respective circuits have different combinations oftheir filter coefficients a and their window sizes similarly to those ofthe horizontal-direction estimation value generating circuit 62.

Therefore, the estimation values E₁ to E₁₂ generated by the respectivecircuits are different from one another.

FIG. 5B shows the filter coefficients a and the window sizes both ofwhich are respectively set for the first vertical-direction estimationvalue generating circuit 62a to the twelfth horizontal-directionestimation value generating circuit 62l.

The vertical-direction estimation value generating circuit 63 accordingto this embodiment has plural kinds of preset windows shown in FIG. 6B.A window W7 is a window of 120 pixels×80 pixels. A window W8 is a windowof 120 pixels×60 pixels. A window W9 is a window of 240 pixels×160pixels. A window W10 is a window of 240 pixels×120 pixels. A window W3is a window of 480 pixels×320 pixels. A window W3 is a window of 480pixels×240 pixels.

It is possible to generate different estimation values corresponding tothe respective combinations of filter coefficients and windows byproviding circuits having a plurality of filter characteristics and aplurality of windows as described above. Therefore, since the estimationvalue is totally generated from a plurality of estimation valuesregardless of an image pickup state of an object to be brought intofocus, it is possible to obtain a precise total estimation value even ifany one of the estimation values is not proper.

Therefore, according to this embodiment, since the focus control circuithas twenty-four estimation value generating circuits for generatingtwenty-four kinds of estimation values obtained from combination oftwelve window sizes and two filter coefficients, it is possible toobtain plural kinds of estimation values. Moreover, since the estimationvalue is totally obtained based on the respective estimation values, itis possible to improve the accuracy of the estimation value.

The microcomputer 64 will be described with respect to FIGS. 2 and 7.

The microcomputer 64 is a circuit for receiving twenty-four estimationvalues E₁ to E₂₄ generated by the horizontal-direction estimation valuegenerating circuit 62 and the vertical-direction estimation valuegenerating circuit 63 and for calculating, based on these twenty-fourestimation values, the direction in which the lens is to be moved and alens position where the estimation value is maximum, i.e., a lensposition where the lens is in focus.

The microcomputer 64 has a ROM 65 which stores a program used forcalculating the twenty-four estimation values in accordance with apredetermined flowchart. As shown in FIG. 7, the ROM 65 storestwenty-four weight data W_(i) corresponding to the respectivetwenty-four estimation values E_(i) (i=1, 2, . . . 24) output from thetwenty-four estimation value generating circuits (62a to 62l and 63a to63l). These weight data W_(i) are data used for giving priority to thetwenty-four estimation values E_(i). The higher values the weight dataW_(i) have, the higher priority the corresponding estimation value E_(i)have. The weight data W_(i) have fixed values preset upon shipment froma factory.

The microcomputer 64 has a RAM 66 for storing the twenty-four estimationvalues E_(i) (i=1, 2, . . . 24) respectively supplied from thetwenty-four estimation value generating circuits (62a to 62l and 63a to63l) in connection with the position of the focus lens. It is assumedthat estimation values generated when the lens is located at a positionX₁ are represented by E₁ (X₁) to E₂₄ (X₁). Initially, the estimationvalues E₁ (X₁) to E₂₄ (X₁) generated when the lens is located at aposition X₁ are stored in the RAM 66. Further, when the lens is movedfrom the position X₁ to a position X₂, estimation values E₁ (X₂) to E₂₄(X₂) generated when the lens is moved to the position X₂ are stored in aRAM 66. Since the RAM 66 stores data in a ring buffer system, thepreviously stored estimation values E₁ (X₁) to E₂₄ (X₁) are not eraseduntil the RAM becomes full of stored data. These estimation values E_(i)are stored in the RAM 64 when designation of a pointer by themicrocomputer 64.

An autofocus operation will be described with reference to FIGS. 8 to 13which are flowcharts therefor and FIG. 14.

A focus mode is shifted from a manual focus mode to an autofocus modewhen a camera man presses an autofocus button provided in an operationbutton 5. The autofocus mode includes a continuous mode in which theautofocus mode is continued after the button is pressed until a commandof mode shift to the manual focus mode is issued, and a non-continuousmode in which, after an object is brought into focus, the autofocus modeis stopped and the mode is automatically shifted to the manual focusmode. The continuous mode will be described in the following explanationwith reference to the flowcharts. In processings in steps S100 to S131,it is determined to which direction the lens is to be moved. Inprocessings in steps S201 to S221, the lens position is calculated sothat the estimation value should be maximum.

As shown in FIG. 14, in steps S100 to S104, based on a command from theCPU 4, the focus lens is moved to the position X₁ which is distant inthe Far direction from an initial lens position X₀ by a distance of D/2,subsequently moved to a position X₂ which is distant in the Neardirection from the position X₁ by a distance of D, and then moved to aposition which is distant from the position X₂ in the Far direction by adistance of D/2, i.e., returned to the initial lens position X₀. TheNear direction depicts a direction in which the lens is moved toward theimaging devices, and the Far direction depicts a direction in which thelens is moved away from the imaging devices. Reference symbol D depictsa focal depth. The microcomputer 64 stores in the RAM 66 the estimationvalues Ei(X₀), the estimation values E_(i) (X₁), and the estimationvalues E_(i) (X₂) generated in the horizontal-direction estimation valuegenerating circuit 62 and the vertical-direction estimation valuegenerating circuit 63.

The reason for preventing the focus lens from being moved from theposition X₀ by a distance exceeding D/2 will be described. The focaldepth is a data indicating a range within which the lens is in focusaround a focus point. Therefore, even if the focus lens is moved withinthe range of the focal depth, then it is impossible for a man torecognize deviation of focus resulting from such movement. Contrary,when the lens is moved from the position X₁ to the position X₂, if thelens is moved by a distance exceeding the focal depth, then deviation ofthe focus resulting from the movement influences the video signalobtained by image pickup. Specifically, when a maximum movement amountof the lens is set within the focal depth, the deviation of the focuscannot be recognized.

The processing in each of steps S100 to S104 will be described in detailwith reference to FIG. 4.

In step S100, the microcomputer 64 stores in the RAM 66 the estimationvalues E₁ (X₀) to the estimation values E₂₄ (X₀) newly generated by thehorizontal-direction estimation value generating circuit 62 and thevertical-direction estimation value generating circuit 63. Afterfinishing storing the above estimation values, the microcomputer 64issues to the CPU 4 a command to move the focus lens in the Fardirection by a distance of D/2.

In step S101, the CPU 4 outputs a command to the focus-lens motor drivecircuit 12c to move the focus lens in the Far direction by a distance ofD/2.

In step S102, the microcomputer 64 stores in the RAM 66 the estimationvalues E₁ (X₁) to the estimation values E₂₄ (X₁) newly generated by thehorizontal-direction estimation value generating circuit 62 and thevertical-direction estimation value generating circuit 63. Afterfinishing storing the above estimation values, the microcomputer 64issues to the CPU 4 a command to move the focus lens in the Neardirection by a distance of D.

In step S103, the CPU 4 outputs a command to the focus-lens motor drivecircuit 12c to move the focus lens in the Near direction by a distanceof D.

In step S104, the microcomputer 64 stores in the RAM 66 the estimationvalues E₁ (X₂) to the estimation values E₂₄ (X₂) newly generated by thehorizontal-direction estimation value generating circuit 62 and thevertical-direction estimation value generating circuit 63. Afterfinishing storing the above estimation values, the microcomputer 64issues to the CPU 4 a command to move the focus lens in the Neardirection by a distance of D/2.

Therefore, when the processing in step S104 is finished, the estimationvalues E₁ (X₀) to the estimation values E₂₄ (X₀) generated when the lensis located at the position X₀, the estimation values E₁ (X₁) to theestimation values E₂₄ (X₁) generated when the lens is located at theposition X₁, and the estimation values E₁ (X₂) to the estimation valuesE₂₄ (X₂) generated when the lens is located at the position X₀ arestored in the RAM 66 of the microcomputer 64.

Processings in steps S105 to S115 are processings for selecting animproper estimation value from the twenty-four estimation values.

A basic concept of operations in steps S105 to S115 will be describedwith reference to FIG. 15A and FIG. 15B. FIGS. 15A and 15B show that atarget object A to be brought into focus is imaged in a window W2 and anon-target object B having high contrast and located on the front sideof the target object A is imaged in a window W1 but outside of thewindow W2. At this time, since the object B exists within the window W1,the estimation value E₁ generated by the first horizontal-directionestimation value generating circuit 62a having a preset window sizevalue of the window W1 inevitably includes high-frequency componentsresulting from the object B and hence is improper as the estimationvalue of the object A. Therefore, the estimation value E₁ inevitablybecomes considerably large as compared with the estimation value E₂generated by the second horizontal-direction estimation value generatingcircuit 62b having the preset value of the window W2. Similarly, theestimation value E₇ generated by the seventh horizontal-directionestimation value generating circuit 62g having a preset window sizevalue of the window W₁ inevitably includes high-frequency componentsresulting from the object B and hence is improper as the estimationvalue of the object A. Therefore, the estimation value E₇ inevitablybecomes considerably large as compared with the estimation value E₈generated by the eighth horizontal-direction estimation value generatingcircuit 62h having the preset value of the window W2.

It is not always determined that the estimation value E₂ or theestimation value E₈ is proper on the basis of only the fact that thenon-target object B does not exist in the window W2. The reason for thiswill be described with reference to FIG. 15B. FIG. 15B shows windowsobtained when the lens is moved so as to be focused on the object A. Themore the lens is adjusted so as to be focused on the object A, the morethe lens becomes considerably out of focus with respect to the object B.When the lens becomes considerably out of focus with respect to theobject B, an image of the object B becomes blurred considerably and theblurred image thereof enters the window W2. Therefore, in a state shownin FIGS. 15A and 15B, the estimation value E₂ generated by the secondhorizontal-direction estimation value generating circuit 62b having thepreset value of the window W2 is not always proper. Similarly, theestimation value E₈ generated by the eighth horizontal-directionestimation value generating circuit 62h having the preset value of thewindow W2 is not always proper.

As described above, in order to determine whether or not the estimationvalues E₁ and E₇ obtained from the window W₁ and the estimation valuesE₂ and E₈ obtained from the window W2 are proper, it is sufficient todiscriminate whether or not

    |E.sub.1 -E.sub.2 |≦E.sub.1 ×β

and

    |E.sub.7 -E.sub.8 |≦E.sub.7 ×β(3)

are satisfied. βis a coefficient previously set based on an experimentalresult. While in this embodiment the value thereof is set to β=0.01, ifpredetermined values obtained from experiments are used instead of (E₁×β) and (E₇ ×β), it is possible to obtain the same result without (E₁×β) and (E₇ ×β) being used in the equation (3).

In the determination based on the calculated result of the equation (3),if both of values of |E₁ -E₂ | and |E₇ -E₈ | are smaller than apredetermined value, then it can be determined that there is almost nodifference between the estimation values E₁ and E₂ and it can bedetermined that there is almost no difference between the estimationvalues E₇ and E₈. Therefore, it is determined that there is no objectsuch as the non-target object B shown in FIG. 15. If both of values of|E₁ -E₂ | and |E₇ -E₈ | are larger than a predetermined value, then itcan be determined that there is some difference between the estimationvalues E₁ and E₂ and it can be determined that there is some differencebetween the estimation values E₇ and E₈. Therefore, it is determinedthat there is an object such as the non-target object B shown in FIG.15. Specifically, when the equation (3) is calculated, if the equation(3) is satisfied, then the estimation values E₁ and E₂ and theestimation values E₇ and E₈ are proper. If on the other hand theequation (3) is not satisfied, then each of the estimation values E₁ andE₂ and the estimation values E₇ and E₈ is not proper.

In consideration of the above basic concept, the processings in stepsS105 to S115 will specifically be described with reference to FIGS. 8and 9.

In step S105, it is determined by using the estimation values E₁ (X₀) toE₂₄ (X₀) obtained when the lens is located at the position X₀ whether ornot

    |E.sub.1 (X.sub.0)-E.sub.2 (X.sub.0)|≦E.sub.1 (X.sub.0)×β.sub.1

and

    |E.sub.7 (X.sub.0)-E.sub.8 (X.sub.0)|≦E.sub.7 (X.sub.0)×β.sub.1                              (105)

are satisfied. If the estimation values E₁, E₂, E₇, E₈ satisfy theequation (105), then it is determined that the estimation values E₁, E₂,E₇, E₈ are proper values, and then the processing proceeds to step S117.If on the other hand the estimation values E₁, E₂, E₇, E₈ do not satisfythe equation (105), then it is determined that at least the estimationvalues E₁, E₂, E₇, E₈ are improper values, and then the processingproceeds to step S106.

Since it is determined based on the calculated result of step S105 thatthe estimation values E₁, E₂, E₇, E₈ are improper, in step S106, theestimation values E₃ and E₉ obtained from the window W3 which is a largewindow next to the window W1 are used and the estimation values E₄ andE₁₀ obtained from the window W4 which is a large window next to thewindow W2 are used.

In step S106, similarly to step S105, it is determined by using theestimation values E₁ (X₀) to E₂₄ (X₀) obtained when the lens is locatedat the position X₀ whether or not

    |E.sub.3 (X.sub.0)-E.sub.4 (X.sub.0)|≦E.sub.3 (X.sub.0)×β.sub.1

and

    |E.sub.9 (X.sub.0)-E.sub.10 (X.sub.0)|≦E.sub.9 (X.sub.0)×β.sub.1                              (106)

are satisfied. If the estimation values E₃, E₄, E₉, E₁₀ satisfy theequation (106), then it is determined that the estimation values E₃, E₄,E₉, E₁₀ are proper values, and then the processing proceeds to stepS107. If on the other hand the estimation values E₃, E₄, E₉, E₁₀ do notsatisfy the equation (106), then it is determined that at least theestimation values E₃, E₄, E₉, E₁₀ are improper values, and then theprocessing proceeds to step S108.

The reason for employing the windows W3 and W4 having larger sizes willbe described. As described above, since the estimation values E₁ and E₂and the estimation values E₇ and E₈ are improper in the state shown inFIG. 14, it is impossible to bring either the target object A or thenon-target object B into focus. However, when the windows W3 and W4larger than the windows W1 and W2 are used, it is considered that thenon-target object B lies in the range of the window W4. If the wholenon-target object B lies within the window W4, then difference betweenthe estimation value E₃ and the estimation value E₄ becomes small anddifference between the estimation value E₉ and the estimation value E₁₀becomes small. Specifically, it is determined that the estimation valuesE₃, E₄, E₉, and E₁₀ satisfy the equation (106). As a result, since theestimation values E₃, E₄, E₉, and E₁₀ become proper values, thenon-target object B is brought into focus. Indeed, the lens should befocused on the target object A. But, if the lens is adjusted so as to befocused on the object A, then it is impossible to obtain the properestimation values. As a result, the autofocus control circuit 34repeatedly executes the processing of a control loop and keeps the focuslens moving for a long time. Therefore, while the autofocus controlcircuit repeatedly executes the control loop, the video signalindicative of a blurred image must continuously be output. However, ifthe lens is focused on the non-target object B, then it is possible toprevent the video signal indicative of the blurred image from beingoutput continuously by repeating the control loop for a long period oftime.

In step S107, numbers of i=1, 2, 7, 8 are defined as non-use numbersbased on the result in step S105 that the estimation values E₁, E₂, E₇,and E₈ are improper values and on the result in step S106 that theestimation values E₃, E₄, E₉, and E₁₀ are proper values. Then, theprocessing proceeds to step S117. Since in step S107 the numbers of i=1,2, 7, 8 are defined as the non-use numbers, the estimation values E₁,E₂, E₇, and E₈ will not be used in step S107 and the succeeding steps.

In step S108, since it is determined based on the result of thecalculation in step S106 that the estimation values E₃, E₄, E₉, and E₁₀are improper, the estimation values E₅ and E₁₁, obtained from the windowW5 which is large next to the window W3 are used and the estimationvalues E₆ and E₁₂ obtained from the window W6 which is large next to thewindow W4 are used.

In step S108, similarly to step S106, it is determined by using theestimation values E₁ (X₀) to E₂₄ (X₀) generated when the lens is locatedat the position X₀, whether

    |E.sub.5 (X.sub.0)-E.sub.6 (X.sub.0)|≦E.sub.5 (X.sub.0)×β.sub.1

and

    |E.sub.11 (X.sub.0)-E.sub.12 (X.sub.0)|≦E.sub.11 (X.sub.0)×β.sub.1                              (108)

are satisfied. If the estimation values E₅, E₆, E₁₁, E₁₂ satisfy theequation (108), then it is determined that the estimation values E₅, E₆,E₁₁, E₁₂ are proper values, and then the processing proceeds to stepS109. If on the other hand the estimation values E₅, E₆, E₁₁, E₁₂ do notsatisfy the equation (108), then it is determined that at least theestimation values E₅, E₆, E₁₁, E₁₂ are improper values, and then theprocessing proceeds to step S110.

In step S109, only numbers of i=1, 2, 3, 4, 7, 8, 9, 10 are defined asnon-use numbers based on the result in step S105 that the estimationvalues E₁, E₂, E₇, and E₈ are improper values, on the result in stepS106 that the estimation values E₃, E₄, E₉, and E₁₀ are improper values,and on the result in step S108 that the estimation values E₅, E₆, E₁₁,and E₁₂ are proper values. Then, the processing proceeds to step S117.Since in step S109 the numbers of i=1, 2, 3, 41 7, 8, 9, 10 are definedas the non-use numbers, the estimation values E₁, E₂, E₃, E₄, E₇, E₈, E₉and E₁₀ will not be used in step S109 and the succeeding steps.

In step S108, since it is determined based on the result of thecalculation in step S106 that the estimation values E₃, E₄, E₉, and E₁₀are improper, the estimation values E₅ and E₁₁ obtained from the windowW5 which is large next to the window W3 are used and the estimationvalues E₆ and E₁₂ obtained from the window W6 which is large next to thewindow W4 are used.

In step S110, similarly to step S108, it is determined by using theestimation values E₁ (X₀) to E₂₄ (X₀) generated when the lens is locatedat the position X₀, whether

    |E.sub.13 (X.sub.0)-E.sub.14 (X.sub.0)|≦E.sub.13 (X.sub.0)×β.sub.2

and

    |E.sub.19 (X.sub.0)-E.sub.20 (X.sub.0)|≦E.sub.19 (X.sub.0)×β.sub.2                              (110)

are satisfied. If the estimation values E₁₃, E₁₄, E₁₉, E₂₀ satisfy theequation (110), then it is determined that the estimation values E₁₃,E₁₄, E₁₉, E₂₀ are proper values, and then the processing proceeds tostep S111. If on the other hand the estimation values E₁₃, E₁₄, E₁₉, E₂₀do not satisfy the equation (110), then it is determined that at leastthe estimation values E₁₃, E₁₄, E₁₉, E₂₀ are improper values, and thenthe processing proceeds to step S112.

In step S111, only numbers of i=1 to 12 are defined as non-use numbersbased on the result in step S105 that the estimation values E₁, E₂, E₇,and E₈ are improper values, on the result in step S106 that theestimation values E₃, E₄, E₉, and E₁₀ are improper values, on the resultin step S108 that the estimation values E₅, E₆, E₁₁, and E₁₂ areimproper values, and on the result in step S110 that the estimationvalues E₁₃, E₁₄, E₁₉, and E₂₀ are proper values. Then, the processingproceeds to step S117. Since in step S111 the numbers of i=1 to 12 aredefined as the non-use numbers, the estimation values E₁ to E₁₂ will notbe used in step S111 and the succeeding steps.

In step S112, similarly to step S110, it is determined by using theestimation values E₁ (X₀) to E₂₄ (X₀) generated when the lens is locatedat the position X₀, whether

    |E.sub.15 (X.sub.0)-E.sub.16 (X.sub.0)|≦E.sub.15 (X.sub.0)×β.sub.2

and

    |E.sub.21 (X.sub.0)-E.sub.22 (X.sub.0)|≦E.sub.21 (X.sub.0)×β.sub.2                              (112)

are satisfied. If the estimation values E₁₅, E₁₆, E₂₁, E₂₂ satisfy theequation (112), then it is determined that the estimation values E₁₅,E₁₆, E₂₁, E₂₂ are proper values, and then the processing proceeds tostep S113. If on the other hand the estimation values E₁₅, E₁₆, E₂₁, E₂₂do not satisfy the equation (112), then it is determined that at leastthe estimation values E₁₅, E₁₆, E₂₁, E₂₂ are improper values, and thenthe processing proceeds to step S114.

In step S113, only numbers of i=1 to 14, 19 and 20 are defined asnon-use numbers based on the result in step S105 that the estimationvalues E₁, E₂, E₇, and E₈ are improper values, on the result in stepS106 that the estimation values E₃, E₄, E₉, and E₁₀ are improper values,on the result in step S108 that the estimation values E₅, E₆, E₁₁, andE₁₂ are improper values, on the result in step S110 that the estimationvalues E₁₃, E₁₄, E₁₉, and E₂₀ are improper values, and on the result instep S112 that the estimation values E₁₅, E₁₆, E₂₁, and E₂₂ are propervalues. Then, the processing proceeds to step S117. Since in step S113the numbers of i=1 to 12, 19 and 20 are defined as the non-use numbers,the estimation values E₁ to E₁₄, E₁₉ and E₂₀ will not be used in stepS113 and the succeeding steps.

In step S114, similarly to step S110, it is determined by using theestimation values E₁ (X₀) to E₂₄ (X₀) generated when the lens is locatedat the position X₀, whether

    |E.sub.17 (X.sub.0)-E.sub.18 (X.sub.0)|≦E.sub.17 (X.sub.0)×β.sub.2

and

    |E.sub.23 (X.sub.0)-E.sub.24 (X.sub.0)|≦E.sub.23 (X.sub.0)×β.sub.2                              (114)

are satisfied. If the estimation values E₁₇, E₁₈, E₂₃, E₂₄ satisfy theequation (114), then it is determined that the estimation values E₁₇,E₁₈, E₂₃, E₂₄ are proper values, and then the processing proceeds tostep S115. If on the other hand the estimation values E₁₇, E₁₈, E₂₃, E₂₄do not satisfy the equation (114), then it is determined that at leastthe estimation values E₁₇, E₁₈, E₂₃, E₂₄ are improper values, and thenthe processing proceeds to step S116.

In step S115, only numbers of i=1 to 16 and 19 to 22 are defined asnon-use numbers based on the result in step S105 that the estimationvalues E₁, E₂, E₇, and E₈ are improper values, on the result in stepS106 that the estimation values E₃, E₄, E₉, and E₁₀ are improper values,on the result in step S108 that the estimation values E₅, E₆, E₁₁, andE₁₂ are improper values, on the result in step S110 that the estimationvalues E₁₃, E₁₄, E₁₉, and E₂₀ are improper values, on the result in stepS112 that the estimation values E₁₅, E₁₆, E₂₁, and E₂₂ are impropervalues, and on the result in step S114 that the estimation values E₁₇,E₁₈, E₂₃, and E₂₄ are proper values. Then, the processing proceeds tostep S117. Since in step S115 the numbers of i=1 to 16 and 19 to 22 aredefined as the non-use numbers, the estimation values E₁ to E₁₆ and E₁₉to E₂₂ will not be used in step S115 and the succeeding steps.

When the processing reaches step S116, it is inevitably determined thatall the estimation values E₁ to E₂₄ are improper. Therefore, it isdetermined that the autofocus operation cannot be carried out. Then, themode is shifted to the manual focus mode and the processing is ended.

Then, the processings in steps for selecting the improper estimationvalues from the twenty-four estimation values is ended.

As shown in FIGS. 10 and 11, processings in steps S117 to S131 are thosein flowcharts for a specific operation for determining the lens movementdirection.

In step S117, the number is set to i=1 and a count-up value U_(cnt), acount-down value D_(cnt) and a flat count value F_(cnt) are reset.

In step S118, it is determined whether or not the number i is a numberdefined as a non-use number. If it is determined that the number i isnot defined as the non-use number, then the processing proceeds to stepS120. If it is determined that the number i is defined as the non-usenumber, then in step S119 the number i is incremented and then the nextnumber of i is determined.

A processing in step S120 is a processing carried out when theestimation value E_(i) (X₀) has not a value substantially equal to E_(i)(X₂) but a value larger than E_(i) (X₂) to some degree and when theestimation value E₁ (X₁) has not a value substantially equal to E_(i)(X₀) but a value larger than E_(i) (X₀) to some degree. To facilitatethis processing further, the processing is that of determining, if thefocus lens is moved in the Far direction from the position X₂ throughthe position X₀ to the position X₁, whether or not the estimation valuesare increased in an order of the estimation values E_(i) (X₂), E_(i)(X₀), E_(i) (X₁). Specifically, it is determined by calculating thefollowing equations;

    E.sub.i (X.sub.2)×β.sub.3 <E.sub.i (X.sub.0)

and

    E.sub.i (X.sub.0)×β.sub.3 <E.sub.i (X.sub.1)    (120)

where β₃ is a coefficient experimentally obtained and set to β₃ =1.03 inthis embodiment. If the above estimation values satisfy the equation(120), it means that as the focus lens is moved from the position X₂through the position X₀ to the position X₁, the estimation values areincreased in an order of the estimation values corresponding thereto.Then, the processing proceeds to the next step S121. If the aboveestimation values do not satisfy the equation (120), then the processingproceeds to step S122.

In step S121, the count-up value U_(cnt) is added with the weight dataWi, and then the processing proceeds to step S126.

A processing in step S122 is a processing carried out when theestimation value E_(i) (X₀) has not a value substantially equal to E_(i)(X₁) but a value larger than E_(i) (X₁) to some degree and when theestimation value E_(i) (X₂) has not a value substantially equal to E_(i)(X₀) but a value larger than E_(i) (X₀) to some degree. To facilitatethis processing further, the processing is that of determining, if thefocus lens is moved in the Far direction from the position X₂ throughthe position X₀ to the position X₁, whether or not the estimation valuesare decreased in an order of the estimation values E_(i) (X₂), E_(i)(X₀), E_(i) (X₁). Specifically, it is determined by calculating thefollowing equations;

    E.sub.i (X.sub.1)×β.sub.3 <E.sub.i (X.sub.0)

and

    E.sub.i (X.sub.0)×β.sub.3 <E.sub.i (X.sub.2)    (122).

If the above estimation values satisfy the equation (122), it means thatas the focus lens is moved from the position X₂ through the position X₀to the position X₁, the estimation values are decreased in an order ofthe estimation values corresponding thereto. Then, the processingproceeds to the next step S123. If the above estimation values do notsatisfy the equation (122), then the processing proceeds to step S124.

In step S123, the count-down value D_(cnt) is added with the weight dataWi, and then the processing proceeds to step S126.

A processing in step S124 is a processing carried out when theestimation value E_(i) (X₀) has not a value substantially equal to E_(i)(X₁) but a value larger than E_(i) (X₁) to some degree and when theestimation value E_(i) (X₀) has not a value substantially equal to E_(i)(X₂) but a value larger than E_(i) (X₂) to some degree. To facilitatethis processing further, the processing is that of determining, if thefocus lens is moved in the Far direction from the position X₂ throughthe position X₀ to the position X₁, whether the peak of the estimationvalues lies in the estimation value E_(i) (X₀). Specifically, it isdetermined by calculating the following equations;

    E.sub.i (X.sub.1)×β.sub.3 <E.sub.i (X.sub.0)

and

    E.sub.i (X.sub.2)×β.sub.3 <E.sub.i (X.sub.0)    (124).

If the above estimation values satisfy the equation (124), it means thatwhen the focus lens is moved from the position X₂ through the positionX₀ to the position X₁, the peak value of the estimation values is theestimation value E_(i) (X₀). Then, the processing proceeds to the nextstep S125. If the above estimation values do not satisfy the equation(120), then the processing proceeds to step S126.

In step S125, the flat-count value F_(cnt) is added with the weight dataWi, and then the processing proceeds to step S126.

In step S126, the number of i is incremented, and then the processingproceeds to step S127.

In step S127, it is determined whether or not the number of i is 24because the horizontal-direction estimation value generating circuit 62and the vertical-direction estimation value generating circuit 63generate the twenty-four estimation values E. If the value of i is 24,then it is determined that calculations of all the estimation values arefinished, and then the processing proceeds to step S128. If the value ofi is not 24, then the processing loop formed of steps S118 to S127 isrepeatedly carried out.

In step S128, it is determined by comparing the count-up value U_(cnt),the count-down value D_(cnt) and the flat-count value F_(cnt), which isthe largest value among the above count values. If it is determined thatthe count-up value U_(cnt) is the largest, then the processing proceedsto step S129. If it is determined that the count-down value D_(cnt) isthe largest, then the processing proceeds to step S130. If it isdetermined that the flat-count value F_(cnt) is the largest, then theprocessing proceeds to step S131.

In step S129, the microcomputer 64 determines that the direction towardthe position X₁ is the hill-climbing direction of the estimation value,i.e., the direction in which the lens is to be in focus, and thensupplies to the CPU 4 a signal designating the Far direction as the lensmovement direction.

In step S130, the microcomputer 64 determines that the direction towardthe position X₂ is the hill-climbing direction of the estimation value,i.e., the direction in which the lens is to be in focus, and thensupplies to the CPU 4 a signal designating the Near direction as thelens movement direction.

In step S131, the microcomputer 64 determines that the position X₀ isthe position at which the lens is in focus, and then the processingproceeds to step S218.

The operations in steps S118 to S131 will plainly be described withreference to the example shown in FIG. 15. FIG. 15 is a diagram showingtransition of change of the estimation values E_(i) (X₂), E_(i) (X₀),E_(i) (X₁) respectively obtained when the lens is located at the lenspositions X₂, X₀, X₁, by way of example.

Initially, it is determined in step S118 whether or not the number of iis the non-use number. In this case, it is assumed that all the numbersof i are numbers of the estimation values which can be used.

In the first processing loop, the estimation values E₁ are estimated.Since E₁ (X₂)<E₁ (X₀)<E₁ (X₁) is established, then this relationshipsatisfies the condition in step S120 and hence the processing proceedsto step S121. Therefore, in step S121, the calculation of U_(cnt) =0+W₁is carried out.

In the second processing loop, the estimation values E₂ are estimated.Since E₂ (X₂)<E₂ (X₀)<E₂ (X₁) is established, then this relationshipsatisfies the condition in step S120 and hence the processing proceedsto step S121. Therefore, in step S121, the calculation of U_(cnt) =W₁+W₂ is carried out.

In the third, fourth and fifth processing loops, the calculationssimilar to those carried out in the first and second processing loopsare carried out. In step S121 of the fifth processing loop, thecalculation of U_(cnt) =W₁ +W₂ +W₃ +W₄ +W₅ is carried out.

In the sixth processing loop, the estimation values E₆ are estimated.Since E₂ (X₂)<E₂ (X₀)>E₂ (X₁) is established, then this relationshipsatisfies the condition in step S124 and hence the processing proceedsto step S125. Therefore, in step S125, the calculation of F_(cnt) =0+W₆is carried out.

After the processing loops are repeatedly carried out twenty-four timesas described above, finally the calculation of

U_(cnt) =W₁ +W₂ +W₃ +W₄ +W₅ +W₇ +W₈ +W₉ +W₁₁ +W₁₃ +W₁₄ +W₁₅ +W₁₇ +W₁₈+W₂₁ +W₂₄

D_(cnt) =W₁₀ +W₁₆ +W₂₂

F_(cnt) =W₆ +W₁₂ +W₁₉

has been carried out. If the values of the weight data W_(i) shown inFIG. 7 by way of example are substituted for the above count-up valueU_(cnt), the above count-down value D_(cnt) and the above flat countvalue F_(cnt), then the following results are obtained.

U_(cnt) =124

D_(cnt) =13

F_(cnt) =18

Therefore, since the count-up value U_(cnt) has the largest value amongthem at the time of determination in step S128, the processing proceedsto step S129 in the example shown in FIG. 15. As a result, the directiontoward X₁ is determined as the focus direction.

Processings in steps S200 to S221 are those for determining the lensposition at which the estimation value becomes maximum. The processingswill be described with reference to FIGS. 11, 12, 13 and 14.

For clear explanation of the processings in step S200 and the succeedingsteps, the following equations are defined. ##EQU1##

Since the estimation value is sampled in every field in this embodiment,a distance depicted by ΔX is defined as a distance by which the focuslens is moved in one field. Therefore, the distance ΔX depicts thedistance by which the lens is moved in one field period. This distanceΔX not only depicts the distance by which the lens is moved in one fieldperiod but also has a polarity of ΔX determined based on the lensmovement direction obtained in the processing in steps S100 to S130. Forexample, if the lens movement direction is the Far direction, the valueof the distance ΔX is set so as to have a positive polarity. If the lensmovement direction is the Near direction, the value of the distance ΔXis set so as to have a negative polarity.

In step S200, K=1 is set.

In step S201, the microcomputer 64 issues to the CPU 4 a command to movethe lens to a position X_(k). The lens position X_(k) is defined basedon equation (200) as

    X.sub.k =X.sub.0 +k×ΔX

In step S202, the microcomputer 64 stores in the RAM 66 the estimationvalues E₁ (X_(k)) to the estimation values E₂₄ (X_(k)) newly generatedby the horizontal-direction estimation value generating circuit 62 andthe vertical-direction estimation value generating circuit 63. Thetwenty-four estimation values E_(i) are stored as a table shown in FIG.16.

In step S203, i=1 and j=1 are set, and the count-up value U_(cnt), thecount-down value D_(cnt) and the flat count value F_(cnt) are reset.

In step S204, it is determined whether or not the number of i is definedas the non-use number. If the number of i is not defined as the non-usenumber, then the processing proceeds to step S206. If the number of i isdefined as the non-use number, then in step S205 the value of i isincremented and the processing returns to step S204 again.

In step S206, it is determined whether or not the estimation valuesE_(i) (X_(k)) obtained when the focus lens is moved from a positionX_(k-1) to a position X_(k) are increased to a certain degree or more ascompared with the estimation values E_(i) (X_(k-1)). Specifically, it isdetermined based on a calculation of

    E.sub.i (X.sub.k-1)×β.sub.4 <E.sub.i (X.sub.k)  (206)

where β₄ is a coefficient experimentally obtained and is set to β₄ =1.05in this embodiment. The satisfaction of the condition of the equation(206) leads to the fact that the estimation values E_(i) (X_(k)) areincreased to a certain degree or more as compared with the estimationvalues E_(i) (X_(k-1)). In this case, the processing proceeds to thenext step S207. If the condition of the equation (206) is not satisfied,then the processing proceeds to step S209.

In step S207, since the estimation values E_(i) (X_(k)) are increased toa certain degree or more as compared with the estimation values E_(i)(X_(k-1)), a 2-bit data "01" indicative of increase of the estimationvalue is stored in the RAM 66 as a U/D information (up/down information)in connection with the estimation value E_(i) (X_(k)).

In step S208, silarly to step S121, the count-up value Unit is addedwith the weight data W_(i), and then the processing proceeds to stepS214.

In step S209, it is determined whether or not the estimation valuesE_(i) (X_(k)) obtained when the focus lens is moved from the positionX_(k-1) to the position X_(k) are decreased to a certain degree or moreas compared with the estimation values E_(i) (X_(k-1)). Specifically, itis determined based on a calculation of

    E.sub.i (X.sub.k)×β.sub.4 <E.sub.i (X.sub.k-1)  (209)

The satisfaction of the condition of the equation (209) leads to thefact that the estimation values E_(i) (X_(k)) are decreased to a certaindegree or more as compared with the estimation values E_(i) (X_(k-1)).In this case, the processing proceeds to the next step S210. If thecondition of the equation (209) is not satisfied, then the processingproceeds to step S212.

In step S210, since the estimation values E_(i) (X_(k)) are decreased toa certain degree or more as compared with the estimation values E_(i)(X_(k-1)), a 2-bit data "10" indicative of decrease of the estimationvalue is stored in the RAM 66 as the U/D information (up/downinformation) in connection with the estimation value E_(i) (X_(k)).

In step S211, similarly to step S123, the count-down value D_(cnt) isadded with the weight data W_(i), and then the processing proceeds tostep S214.

In consideration of the conditions of the processings in step S206 andS209, the fact that the processing reaches step S212 means that theestimation values E_(i) (X_(k)) obtained when the focus lens is movedfrom the position X_(k-1) to the position X_(k) are not changed to acertain degree or more relative to the estimation values E_(i)(X_(k-1)).

Therefore, in step S212, a 2-bit data "00" indicative of flatness of theestimation value is stored in the RAM 66 as the U/D information (up/downinformation) in connection with the estimation value E_(i) (X_(k)).

In step S213, similarly to step S125, the flat-count value F_(cnt) isadded with the weight data W_(i), and then the processing proceeds tostep S214.

In step S214, the value of i is incremented, and then the processingproceeds to step S215.

In step S215, it is determined whether or not the value of i is 24. Ifit is determined that the value of i is 24, then it is determined thatcalculations of all the estimation values are finished, and then theprocessing proceeds to step S216. If it is determined the value of i isnot 24, then the processing loop from step S204 to step S215 isrepeatedly carried out until the value of i reaches 24.

A processing in step S216 is that for determining whether or not thecount-down value D_(cnt) is the largest among the count values. Theprocessing in step S216 will be described by using an example shown inFIG. 17. FIG. 17 is a table showing a state of the respective estimationvalues and the respective up/down informations stored in the RAM 66. Asshown in FIG. 17, the microcomputer 64 stores in the RAM 66 therespective estimation values and the respective up/down informations setin connection with the former so that these values and informationsshould correspond to the position X_(k) to which the lens is moved.

When the lens is located at the position X_(k), if the processing loopfrom step S204 to step S215 is repeatedly carried out, then the count-upvalue U_(cnt) the count-down value D_(cnt) and the flat-count valueF_(cnt) are as follows.

U_(cnt) =W₁ +W₂ +W₄ +W₅ +W₈ +W₉ +W₁₁ +W₁₄ +W₁₅ +W₁₆ +W₁₉ +W₂₃

D_(cnt) =W₇ +W₁₀ +W₁₇ +W₁₈ +W₂₀ +W₂₁ +W₂₄

F_(cnt) =W₃ +W₆ +W₁₂ +W₁₃ +W₂₂

If the values of the weight data W_(i) shown in FIG. 7 by way of exampleare substituted for the above count-up value U_(cnt), the abovecount-down value D_(cnt) and the above flat count value F_(cnt), thenthe following results are obtained.

U_(cnt) =95

D_(cnt) =34

F_(cnt) =31

Specifically, although a value is increased, decreased or not changeddepending upon each of the values, it is possible to judge inconsideration of all the estimation values that the estimation value isincreased.

An estimation value obtained by a synthetic judgement thus made in stepS216 will hereinafter be referred to as "a total estimation value".Therefore, in other words, the processing in step S216 can be expressedas that for determining whether or not the total estimation value isdecreased.

It will be described how to judge estimation values generated when thelens is located at the position X_(k+1) as shown in FIG. 17 by way ofexample. When the lens is located at the position X_(k+1), if theprocessing loop from step S204 to step S215 is repeatedly carried out,then the count-up value U_(cnt), the count-down value D_(cnt) and theflat-count value F_(cnt) are as follows.

U_(cnt) =W₅ +W₁₁ +W₁₂ +W₁₇ +W₁₈ +W₂₀ +W₂₃

D_(cnt) =W₁ +W₂ +W₃ +W₆ +W₇ +W₈ +W₁₀ +W₁₃ +W₁₄ +W₁₅ +W₁₆ +W₁₉ +W₂₁ +W₂₂+W₂₄

F_(cnt) =W₄ +W₉

If the values of the weight data W_(i) shown in FIG. 7 by way of exampleare substituted for the above count-up value U_(cnt), the abovecount-down value D_(cnt) and the above flat count value F_(cnt), thenthe following results are obtained.

U_(cnt) =29

D_(cnt) =113

F_(cnt) =18

Specifically, study of the above results can lead to determination thatthe total estimation value is decreased. If it is determined in stepS216 that the total estimation value is decreased, then the processingproceeds to step S217.

In step S217, the value of j is incremented, and then the processingproceeds to step S218. This value of j is a value indicative of how manytimes the determination result in step S216 is continuously YES, i.e.,how many times the total estimation value is continuously decreased.

Assuming that the first lens position where the total estimation valuestarts continuously decreasing is the position X_(k+1), it is determinedin step S218 whether or not the lens movement distance (X_(k+j) from theposition X_(k) is larger than D×n. An equation actually used for thedetermination is expressed by

    ΔX×j≧D×n                          (218)

where D depicts a focal depth of the focus lens and n depicts apreviously set coefficient. Study of experimental results reveals thatwhen the value of n is set within the range of 1≦n≦10, the autofocusoperation at an optimum speed can be realized.

A determination carried out in step S218 will be described withreference to FIG. 18. An abscissa of a graph shown in FIG. 18 representsa lens position X, and an ordinate thereof represents an estimationvalue E(X) corresponding to the lens position.

When j=1 is established, the total estimation value is that obtained atthe lens position where the total estimation value is decreased firsttime, and hence the lens position corresponding to j=1 is the lensposition X_(k+1). Therefore, a right side (ΔX×j) of the equation (218)represents the distance between the lens position X_(k) locatedimmediately before the total estimation value has been decreased and thefirst lens position X_(k+1) where the total estimation value startsdecreasing first. However, study of FIG. 18 reveals that the result ofdetermination in step S218 is NO.

When j=2 is established, the total estimation value is that obtained atthe lens position where the total estimation value has been decreasedcontinuously twice, and hence the lens position corresponding to j=2 isthe lens position X_(k+2). Therefore, as shown in FIG. 18, a right side(ΔX×j) of the equation (218) represents the distance between the lensposition X_(k) located immediately before the total estimation value hasbeen decreased and the lens position X_(k+2) where the total estimationvalue has been decreased continuously twice. However, study of FIG. 18reveals that the result of determination in step S218 is NO.

When j=3 is established, the result of determination in step S218 is NOsimilarly to that determined when j=2.

When j=4 is established, the total estimation value is that obtained atthe lens position where the total estimation value has been decreasedcontinuously four times, and hence the lens position corresponding toj=4 is the lens position X_(k+4). Therefore, as shown in FIG. 18, aright side (ΔX×j) of the equation (218) represents the distance betweenthe lens position X_(k) located immediately before the total estimationvalue has been decreased and the lens position X_(k+4) where the totalestimation value has been decreased continuously twice. Accordingly,study of FIG. 18 reveals that (ΔX×j)≧D×n is established and hence theresult of determination in step S218 is YES.

If on the other hand it is determined in step S216 that the count-downvalue D_(cnt) does not have the largest value, then it is determinedthat the total estimation value is not decreased, and then theprocessing proceeds to step S219.

In step S219, the value of i is set to j=0. This processing is that forresetting the value of j. The reason for resetting the value of j isthat j is the value indicative of how many times the total estimationvalue has been decreased continuously. Moreover, since the fact that theprocessing reaches step S219 means that it is determined in step S216that the total estimation value is not decreased, the continuousdecrease of the total estimation value is stopped at the time ofdetermination in step S216. Accordingly, in step S219, the value of j isreset.

Since the value of j is reset when the continuous decrease of the totalestimation value is stopped, even if a certain estimation value E(X_(k))has a maximum value produced simply by a noise in the example shown inFIG. 18, then the value of j is reset in the processing loop for theestimation values E(X_(k+1)) or E(X_(k+2)) or E(X_(k+3)) and hence theestimation value E(X_(k)) is prevented from being estimated as thelargest value.

In step S220, the value of k is incremented in order to further move thefocus lens. Then, the processing returns to step S201.

If the result of the determination in step S218 is YES, then theprocessing proceeds to step S221. In step S221, since the totalestimation value obtained when the lens is located at the lens positionX_(k) has been decreased continuously predetermined times (j times), themicrocomputer 64 determines the lens position X_(k) as a lens positionX_(g) where the estimation value becomes maximum.

Based on the up/down information stored in the RAM 66, the numbers of isatisfying that an up/down state of the estimation value and an up/downstate of the estimation values Ei stored in the RAM 66 are agreed witheach other are selected from the estimation values E_(i) (X_(k))obtained when the lens is located at the lens position X_(k). If aweight data W_(g) is the largest among the weight data W_(i) whosenumbers are selected numbers of i, then an estimation value E_(g)(X_(k)) is defined as the maximum estimation value. When the maximumestimation value E_(g) (X_(k)) is defined, an estimation value E_(g)(X_(k+1)) is defined as a lower limit estimation value corresponding tothe maximum estimation value. While the maximum estimation value E_(g)(X_(k)) is updated in every field even after the lens is fixed at thelens position X_(k) and becomes in focus, the lower limit estimationvalue E_(g) (X_(k+1)) is fixed.

The above processing will be described by using the example shown inFIG. 17. When the lens is located at the lens position X_(k), the totalestimation value is increased based on the determination in step S216.When the lens is located at the lens position X_(k+1), the totalestimation value is decreased based on the determination in step S216.Therefore, the number i of the estimation value whose up/downinformation is increased when the lens is located at the lens positionX_(k) and decreased when the lens is located at the lens positionX_(k+1) is i=1, 2, 5, 8, 14, 15, 19 in the example shown in FIG. 17.Since the number, among the above numbers, corresponding to the largestweight data is i=1 according to the data shown in FIG. 7, the estimationvalue E₁ (X_(k)) is employed as the maximum estimation value.

In step S222, the microcomputer 64 supplies the control signal to theCPU 4 so that the focus lens should be moved to the lens position X_(g)where the estimation value is maximum.

In step S223, it is determined whether or not a command to stop theautofocus mode is issued. If the camera man operates a button to cancelthe autofocus mode, then the processing proceeds to step S224, whereinthe mode is shifted to the manual focus mode.

If it is determined in step S223 that the command to stop the autofocusmode is not issued, then the processing proceeds to step S225, whereinthe maximum estimation value E_(g) (X_(k)) and the lower limitestimation value E_(g) (X_(k+1)) are compared. If the value of themaximum estimation value E_(g) (X_(k)) becomes smaller than the lowerlimit estimation value E_(g) (X_(k+1)) due to change of an object or thelike, then the processing proceeds to step S226, wherein the autofocusmode is restarted.

The operation of the autofocus mode has been described completely.

The present invention achieves the following effects.

Initially, since a plurality of estimation values can be obtained bycombination of a plurality of filter coefficients and a plurality ofwindow sizes, it is possible to handle various objects.

Since the weight data are allocated to the estimation value generatingcircuits and hence the total estimation value can be obtained based onthe plurality of estimation values and the weight data respectivelycorresponding to the estimation values, the accuracy of the estimationvalue finally obtained is improved. As the accuracy of the estimationvalue is improved, the estimation-value curve describes a smoothparabola around the focus point, which allows high speed determinationof the maximum estimation value. Therefore, the autofocus operationitself can be carried out at high speed.

Since the estimation values determined as the improper estimation valueswhen the total estimation value is calculated are selected from theplurality of estimation values and the selected estimation values arenot used for the determination of the total estimation value, theaccuracy of the estimation values is further improved. For example, ifthe proper estimation value cannot be obtained with a small window, thenthe lens is focused on an object by using the estimation valuecorresponding to a window larger than the above small window. Therefore,it is possible to focus the lens on some object, which prevents theautofocus operation from being continued for a long period of time.

Moreover, when the lens movement direction is determined in order tofocus the lens on an object, a plurality of changed estimation valuesare estimated by employing decision by majority thereof and the weightdata. Therefore, it is possible to precisely determine the focusdirection by employing the sampling points of small number and a finemovement in the focal depth of the lens.

When it is determined whether or not the maximum point of the estimationvalue represents the maximum estimation value, the lens is moved fromthe maximum point by a distance which is predetermined times as long asthe focal depth. As a result, even if the hill of the estimation valuesis flat, it is possible to determine whether or not the maximum pointrepresents the maximum estimation value when the lens is moved by apredetermined distance. Therefore, there can be obtained the effect inwhich the focus point can be determined at high speed. For example, itis possible to avoid output of an image which becomes considerablyblurred and strange because the lens becomes considerably out of focuswhen it is determined whether or not the maximum point represents themaximum estimation value.

When the maximum estimation value obtained when the lens is located atthe focus point is calculated, the estimation value satisfying that theup/down state of the total estimation value and the up/down informationstored in the RAM 66 are agreed with each other and having the largestweight data is selected as the maximum estimation value. Therefore, itis possible to achieve the effect in which the precise value of themaximum estimation value can be obtained.

We claim:
 1. A focus control apparatus for focusing, at focus lenspositions, a focus lens on a target object to be imaged,comprising:estimation value generating means for generating anestimation value by extracting a high-frequency component of a videosignal output from an imaging means; detecting means for detectingwhether the estimation value for a particular focus lens positionincreases from a previous estimation value of imaging said targetobject; and control means for detecting a maximum focus lens positionwhere the estimation value generated by said estimation value generatingmeans increases to a maximum, iterating a number of successive focuslens positions succeeding the maximum focus lens position anddetermining that the maximum focus lens position is a correct focus lensposition for focusing said focus lens on said target image when theestimation value of each iterated successive focus lens positionsuccessively decreases.
 2. A focus control apparatus according to claim1, wherein said control means comprises storage means for storing saidestimation value generated by said estimation value generating means ateach focus lens position of said focus lens.
 3. A focus controlapparatus according to claim 2, wherein said storage means firmer storesup/down information indicative of the total that said estimation valuegenerated by said estimation value generating means isincreased/decreased for a plurality of conditions for each focus lensposition of said focus lens.
 4. A focus control apparatus according toclaim 1, wherein said estimation value generating means is formed of aplurality of estimation value generating circuits for generating foreach focus lens position said estimation value for respective conditionsthereby generating a plurality of estimation values for each focus lensposition; wherein said control means detects said correct focus lensposition by comparing said estimation values for different focus lenspositions.
 5. A focus control apparatus according to claim 1, furthercomprising weight means for weighting said estimation value for each ofsaid plurality of conditions at each focus lens position, wherein saiddetecting means detects whether a total estimation value representing asum total of the weighted estimation values for each focus lens positionincreases/decreases/remains unchanged; wherein said detecting meansdetects whether said particular focus lens position increases/decreasesor remains unchanged based on said total estimation value.
 6. A focuscontrol apparatus according to claim 4, wherein said respectiveconditions of imaging include a filter characteristic for extracting ahigh-frequency component of said video signal and a size of a detectionwindow where said focus lens is focused for said video signal.
 7. Afocus control apparatus according to claim 4, wherein said control meansdetermines a direction of movement of said focus lens by discriminatinga direction in which a total estimation value representing a total ofsaid plurality of estimation values for successive focus lens positionsis increased in value when said focus lens is moved forward or backwardwith respect to a focal depth of said focus lens, and then carries out acorrect focus lens detecting processing for detecting said correct focuslens position while said focus lens is moved in said direction ofmovement.
 8. A focus control apparatus according to claim 7, whereinsaid direction of movement is determined by determining a focus lensmovement direction based on said plurality of estimation values obtainedwhen the focus lens is located at an initial focus lens position wheresaid focus lens is located initially, wherein said plurality ofestimation value generating circuits generate said plurality ofestimation values obtained when the focus lens is located at a firstfocus lens position located after movement of said focus lens from saidinitial lens position by a first predetermined distance in a directiontoward said target object, and wherein said plurality of estimationvalue generating circuits generate said plurality of estimation valuesobtained when the focus lens is located at a second focus lens positionlocated after movement of said focus lens from said initial lensposition by a second predetermined distance in a direction toward animaging device for imaging said target object.
 9. A focus controlapparatus according to claim 8, wherein said first and secondpredetermined distances each does not exceed a focal depth of said focuslens.
 10. A focus control apparatus according to claim 4, wherein saidfocus lens receives an image of said target object to be focused and anincorrect object, wherein said control means comprises an estimationvalue determining means for determining whether an estimation valueobtained by said estimation value generating means is a correctestimation value indicative of a focus degree with respect to saiddesired object or an incorrect estimation value indicative of a focusdegree with respect to said incorrect object.
 11. A focus controlapparatus according to claim 4, wherein said plurality of estimationcircuits each has, as a different condition for imaging, a differentdetection window in which said target object is imaged, wherein, if itis determined that a first estimation value obtained by a firstestimation value generating circuit having a first detection window of afirst size is an incorrect estimation value indicative of a focus degreewith respect to said target object to be focused, then said controlmeans employs a second estimation value obtained by a second estimationvalue generating circuit having a second detection window of a sizesignificantly larger than said first size.
 12. A focus control apparatusaccording to claim 4, further comprising a window generating circuit forgenerating detection windows where said focus lens is focused on saidtarget object, wherein said control means comprises estimation valuedetermining means for comparing a first estimation value obtained by afirst estimation value generating circuit for a first detection windowincluding said target object to be focused and a second estimation valueobtained by a second estimation value generating circuit for a seconddetection window including an incorrect object which is not to befocused to thereby determine whether said first estimation value is acorrect estimation value indicative of a focus degree with respect tosaid target object to be focused or an incorrect estimation valueindicative of a focus degree with respect to said incorrect object. 13.A focus control apparatus according to claim 12, wherein, if saidestimation value determining means determines that said first estimationvalue is incorrect indicating that a blurred portion of said incorrectobject extends into said first detection window, then said control meansemploys a third estimation value to determine said correct focus lensposition obtained by a third estimation value generating circuit forgenerating a third estimation value for a third detection windowincluding both said target object and said incorrect object.
 14. A focuscontrol apparatus according to claim 13, wherein said estimation valuedetermining means determines, if a difference between said firstestimation value and said second estimation value is smaller than apredetermined value, that said first estimation value is correct anddetermines, if the difference between said first estimation value andsaid second estimation value is larger than a predetermined value, thatsaid first estimation value is incorrect.
 15. A focus control apparatusaccording to claim 1, wherein said video signal represents a videopicture having video fields, wherein said control means determines adirection of movement in which said estimation value is increased whensaid focus lens is moved by a distance which does not exceed a focaldepth of said focus lens, and then controls said estimation valuegenerating means to generate said estimation value for every field whilesaid focus lens is moved at a predetermined speed selected such thatsaid focus lens is moved by a distance longer than said focal depth fora period of time in which one field is to be displayed.
 16. A focuscontrol apparatus according to claim 4, wherein said video signalrepresents a video picture having video fields, wherein said controlmeans a determines from said plurality of estimation values obtained bysaid plurality of estimation value generating circuits when said focuslens is moved by a distance which does not exceed a focal depth of saidfocus lens to thereby determine a direction of movement in which saidestimation value is increased, controls said plurality of estimationvalue generating means to generate estimation values for every fieldwhile said focus lens is moved at a predetermined speed selected suchthat said focus lens is moved by a distance longer than said focal depthfor a period of time in which one field is to be displayed, anddetermines direction of movement from said plurality of estimationvalues obtained from said plurality of estimation value generatingcircuits for every field, thereby detecting said correct focus lensposition.
 17. A video camera apparatus having an autofocus function forfocusing a focus lens having focus lens positions on a target object,comprising:an estimation value generating means for generating anestimation value by extracting a high-frequency component of a videosignal output from an imaging means; detecting means for detectingwhether the estimation value for a particular focus lens positionincreases from a previous estimation value of imaging said targetobject; and control means for detecting a maximum focus lens positionwhere said estimation value generated by said estimation valuegenerating means increases to a maximum, iterating a number ofsuccessive focus lens positions succeeding the maximum focus lensposition and determining that the maximum focus lens position is acorrect focus lens position for focusing said focus lens on said targetimage when the estimation value of each iterated successive focus lensposition successively decreases.
 18. A focus control method of focusinga focus lens, having focus lens positions, on a target object comprisingthe steps of:a) generating an estimation value by extracting ahigh-frequency component of a video signal output from an imaging means;b) detecting whether, for a particular focus lens position, that saidestimation value generated in said step a) increases from a previousestimation value of imaging said target object; c) determining a maximumfocus lens position where said estimation value increases to a maximum,iterating a number of successive focus lens positions succeeding themaximum focus lens position and determining that the maximum focus lensposition is a correct focus lens position for focusing said focus lenson said target image when the estimation value of each iteratedsuccessive focus lens position successively decreases; and d) movingsaid focus lens to said correct focus lens position.
 19. The focuscontrol method according to claim 18, comprising the step of storingsaid estimation value generated in said step a) for each of saidplurality of conditions at each focus lens position of said focus lens.20. The focus control method according to claim 19, further comprisingthe step of storing up/down information indicative of the total thatsaid estimation value generated in said step a) is increased/decreasedfor said plurality of conditions at each focus lens position of saidfocus lens.
 21. The focus control method according to claim 18, furthercomprising the step of weighting said estimation value for each of saidplurality of conditions at each focus lens position, and wherein saidstep b) detects whether a sum total of the weighted estimation valuesfor each focus lens position increases/decreases.
 22. The focus controlmethod according to claim 18, wherein said plurality of conditions ofimaging include a high-frequency component of said video signal and asize of a detection window where said focus lens is focused.
 23. Thefocus control method according to claim 18, further comprising the stepsof generating detection windows where said focus lens is focused on saidtarget object; and comparing a first estimation value obtained for afirst detection window including said target object to be focused and asecond estimation value obtained for a second detection window includingan incorrect object which is not to be focused, wherein a thirdestimation value is generated for a third detection window includingboth said target object and said incorrect object.
 24. The focus controlmethod of claim 18, wherein the focal distance between each focus lensposition is a predetermined multiple of a focal depth of said focuslens.
 25. The focus control apparatus according to claim 1, wherein thefocal distance between each focus lens position is a predeterminedmultiple of a focal depth of said focus lens.
 26. A focus controlapparatus according to claim 1, wherein said control means selects saidnumber of successive focus lens positions within a distance from themaximum focus lens position determined by the product of the focal depth(D) and the number of focus lens positions (n).
 27. A focus controlapparatus according to claim 26, wherein said number of focus lenspositions is set within the range of 1≦n≦10.
 28. A focus controlapparatus according to claim 1, further comprising driving means fordriving said focus lens to successive focus lens positions from aninitial focus lens position to said maximum focus lens position, whereinsaid detecting means detects for each successive focus lens positionwhether the estimation value for the particular focus lens positionincreases from the previous estimation value to the focus lens positionwhere the estimation value generated increases to said maximum.
 29. Afocus control apparatus according to claim 1, wherein said control meansiterates a counter for each successive focus lens position succeedingthe maximum focus lens position.
 30. A focus control apparatus accordingto claim 29, wherein said estimation value generating means generatessaid estimation value for each focus lens position for a plurality ofimaging conditions, thereby generating a plurality of estimation valuesfor each focus lens position; wherein said control means for eachiteration of the counter determines a total estimation value for theplurality of estimation values for each focus lens position whichindicates the overall increase/decrease or unchanged state of theestimation value for a respective focus lens position and determines onthe basis of said total estimation value the maximum focus lens positionwhere the total estimation value increases to a maximum.
 31. A focuscontrol apparatus according to claim 30, wherein said total estimationvalue is determined by summing each estimation value for the respectivefocus lens position for respective up/down or unchanged estimationvalues and said total estimation value for the respective focus lensposition is determined by the largest sum of up/down or unchangedestimation values.
 32. A focus control apparatus according to claim 31,wherein the sums of the up/down or unchanged estimation values for eachfocus lens position are weighted in accordance with the imagingcondition for the respective estimation value such that each sumcomprises a sum of weighted estimation values for the respective focuslens position.
 33. A focus control apparatus according to claim 32,wherein said weights are in accordance with a window size in which saidfocus lens is focused on said target object, and wherein said pluralityof estimation values for the respective focus lens position havedifferent window sizes.
 34. The focus control apparatus according toclaim 33, wherein said weights are filtered coefficients for filteringsaid plurality of estimation values for the respective focus lensposition for each window size.
 35. A focus control apparatus accordingto claim 8, wherein said direction of movement is determined by saidcontrol means preceding the detection of the correct focus lensposition; wherein said control means determines said direction ofmovement by determining a total estimation value indicating an overallincrease/decrease or unchanged value of said successive focus lensposition for said plurality of estimation values.
 36. A focus controlapparatus according to claim 35, wherein said control means weights eachof said plurality of estimation values for the respective focus lensposition, such that said control means forms an increase/decrease orunchanged sum of weighted estimation values and said total estimationvalue of the respective focus lens position is based on an overallestimation value of the increase/decrease or unchanged summation values.37. A focus control apparatus according to claim 36, wherein saidweights are determined by said control means in accordance with aplurality of window sizes for imaging said target object, wherein eachestimation value for said respective focus lens position has a differentwindow size.
 38. A focus control apparatus according to claim 37,wherein said weights are filter coefficients for filtering eachestimation value of the respective focus lens position to generate theplurality of estimation values.